In a manufacturing process for a flat panel display (FPD), to reduce manufacturing costs, a gray-tone mask is used to allow for two or more types of patterning. The gray-tone mask includes a light shield portion, which shields light, a transparent portion, which transmits light, and a semi-transparent portion, which partially transmits light. Gray-tone masks are categorized into a slit mask and a halftone mask in accordance with the structure of the semi-transparent portion.
The semi-transparent portion of a slit mask is formed by forming slits in a light shield layer, which is shared by the light shield portion, with a pitch that is less than or equal to the resolution limit. Enlargement of FPDs have enlarged the mask sizes. This has drastically increased the amount of data required to form the slits. Thus, in a process for manufacturing the slit masks, much time and money is necessary to form the slits. As a result, when manufacturing large FDPs that use slit masks, the cost for manufacturing large FDPs cannot be sufficiently reduced.
The semi-transparent portion of a halftone mask includes a semi-transparent layer that partially transmits light. There are two processes for manufacturing the halftone mask. The first manufacturing process forms a light shield layer on the substrate and etches the light shield layer to form the semi-transparent portion and the transparent portion. The other manufacturing process first sequentially superimposes a semi-transparent layer and a light shield layer on a substrate and then sequentially etches the light shield layer and the semi-transparent layer to form the light shield portion, the semi-transparent portion, and the transparent portion.
In the first manufacturing process, film formation and etching are alternately performed. This prolongs the processing time and makes it difficult to sufficiently reduce the manufacturing cost of the halftone mask. In the other manufacturing process, it is difficult to obtain etching selectivity between the semi-transparent layer and the light shield layer. Thus, it is difficult to obtain the required processing accuracy for the light shield portion and the semi-transparent portion. For this reason, proposals have been made to solve the above problems for the halftone mask manufacturing technology.
Patent document 1 and patent document 2 each sequentially superimpose a semi-transparent layer, an etching stopper layer, and a light shield layer on a substrate and then sequentially etches the light shield layer, the etching stopper layer, and the semi-transparent layer to form the light shield portion, the semi-transparent portion, and the transparent portion. In this case, the presence of the etching stopper layer substantially increases the etching selectivity for the light shield layer and the sere-transparent layer. This improves the processing accuracy of the halftone mask.
In patent document 1 and patent document 2, the material of the etching stopper layer is silicon oxide, silicon nitride, or silicon oxynitride. Alternatively, the material of the etching stopper layer is a metal oxide using a metal such as aluminum, hafnium, or zirconium. These materials each have a high etching selectivity for the light shield layer and the semi-transparent layer. However, to etch the etching stopper layer, these materials each require a dry etching technique, which uses a costly vacuum device, or a wet etching technique, which uses a fluorine etching liquid. As a result, the manufacturing cost is drastically increased when using the dry etching technique and environmental pollution is caused by fluorine exhaust gas when using the fluorine etching liquid. Further, when using the fluorine etching liquid, the management and recovery of the etching liquid is burdensome. This lowers versatility when manufacturing the etching stopper layer.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-189281    Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-154122